Genetic factors play a major role in the etiology of autoimmune thyroid diseases (AITD), Hashimoto's thyroiditis (HT) &Graves'disease (GD). Our hypothesis is that the etiology of AITD depends on interactions between immune regulatory genes and thyroid specific genes. Our goals are to identify the AITD susceptibility genes and to dissect the mechanisms by which they cause disease. Our findings during the last grant period, which are the starting point for the specific aims of this proposal, included: (1) Identifying novel AITD loci which are specific for subsets of AITD (Italian patients, &childhood AITD);(2) Narrowing down two major replicated AITD loci (12q &14q), setting the stage for gene-identification;(3) Discovering a new Kozak sequence SNP in the CD40 gene that predisposes to GD by increasing the translational efficiency of CD40. For the next grant period we propose to build on these finding, and our specific aims are: (1) To identify the AITD susceptibility genes in the two subset specific loci by fine mapping in Italian GD patients, linked to a locus on 3q, and childhood AITD, linked to loci on Xp &10q;the subset-specific AITD genes may represent novel therapeutic targets specific to subgroups of AITD patients;(2) To identify the AITD susceptibility genes in the 2 major replicated loci on 12q &14q by linkage disequilibrium mapping, haplotype analysis, and gene sequencing. (3) To test the hypothesis that the CD40 Kozak SNP predisposes to GD by inducing over-expression of CD40 on antigen presenting cells (APC's), causing augmented immune responsiveness, as well as increasing CD40 expression on thyrocytes, thereby focusing the immune response to the thyroid. In vitro studies: we will examine the effects of the CD40 SNP genotypes on CD40 expression, signaling, and function in thyrocytes and APC's, in order to dissect the effects of the SNP on CD40 expression &function in these cells. In vivo studies: We are generating transgenic mice over-expressing CD40 in the thyroid. These mice will enable us to test, in vivo, the effects of CD40 over-expression in the thyroid on susceptibility to the induction of an experimental GD model. We will also use these mice to test CD40 blockade as a novel therapy for experimental GD. In summary, the current proposal builds directly on the knowledge gained in the previous grant period. Our approach has already been successful in identifying novel disease-associated genes. Establishing the immunogenetic pathways causing thyroid autoimmunity will lead to a better understanding of the basic etiology of AITD. This could have a major impact on public health, as it may facilitate the development of mechanism-based treatments in autoimmunity, such as CD40 blockade.